Recently, sticker-type surface finishing materials such as interior/exterior materials of buildings, interior design materials, advertising materials, and the like, which employ adhesives, have been increasingly used. Conventional oil-based adhesives as the adhesives incur discharge of residual solvents into air for a long period of time after construction and thus residents of buildings suffer symptoms such as headache, eye, nose and throat irritation, cough, itching, dizziness, fatigue, reduction in concentration, and the like and, when exposed to such residual solvents for a long period of time, suffer sick house syndrome that causes respiratory ailments, heart disease, cancer, and the like.
For such reasons, water-based emulsion adhesives, which use water as a dispersion medium, are environmentally friendly, and do not discharge harmful materials, have received much attention and are rapidly replacing conventional oil-based adhesives. Such water-based emulsion adhesives may use polymers having higher molecular weight than that of solvent-based polymers because adhesive viscosity is not related to molecular weights of polymers as dispersions, may have broad concentration ranges of solid content, have low ageing resistance, low viscosity, and good adhesive strength in a low solid content region, and have good compatibility with other polymers.
However, due to use of water as a solvent, such water-based emulsion adhesives have a slow drying rate, low adhesive strength to hydrophobic adhesive surfaces and non-porous materials, narrow ranges of selection of curing agents, and deteriorated initial adhesive strength. In addition, water-based emulsion adhesives include emulsifiers and dispersants and thus have no superior physical properties (e.g., low water resistance and the like) to those of oil-based adhesives.
Meanwhile, pressure sensitive adhesives (PSAs) generally require excellent initial adhesion, adhesion and cohesion and good balance thereamong, and do not cause of damage to and contamination of a surface of a material adhered by a PSA when the PSA is peeled from the material after long-term adhesion. In addition, PSAs requires slightly low, allowable increase in adhesion even at high temperature and high humidity, which enables a PSA to be clearly peeled off even after a long period of adhesion.
However, it is not easy to prepare PSAs with the desired properties described above and, in particular, water-based acrylic adhesives generally have high surface energy and high polarity and thus are adhered very satisfactorily to materials with high surface energy but are adhered relatively poorly to materials with low surface energy. In addition, water-based acrylic adhesives have high shear resistance and thus have excessively high adhesion and poor heat resistance.
To address these problems, the related art discloses technologies employing advantages of silicone-based materials. Korean Patent Application Publication No. 10-2006-0130397 discloses a method of preparing a UV-curable pressure sensitive adhesive composition by polymerizing an acrylic monomer and silicone acrylate using a photoinitiator. Korean Patent Application Publication No. 10-2008-0100819 discloses a method of preparing an adhesive by blending an acrylate copolymer with silica nanoparticles, whereby peel strength of the adhesive is maintained and the adhesive has increased shear strength (holding power) at high temperature. Korean Patent Application No. 10-2009-0025238 discloses a Si-containing pressure sensitive adhesive composition and, in particular, a silicone acrylate hybrid composition including a reaction product of an ethylene-based unsaturated monomer and an initiator and a method of using the silicone acrylate hybrid composition in a transdermal drug delivery system.
However, the adhesive compositions disclosed in the above-described related art do not exhibit satisfactory weather resistance and heat resistance so as to have stable adhesion and high holding power at high temperature and high humidity even after aging.
Thus, there is a high need to develop adhesives that are environmentally friendly and have excellent weather resistance and heat resistance and thus, when being applied to paper and film labels, may maintain high peel strength and high cohesive strength even under high temperature and high humidity conditions.